The objective of the proposed research is to examine the relationship between thalamic and cortical inputs to the striatum from areas which receive basal ganglia output. The striatum functions as the main input nucleus of the basal ganglia and receives inputs primarily from the cerebral cortex, the thalamus and the midbrain. The thalamus provides the second largest source of input to the striatum. In the primate, the striatum receives massive inputs primarily from the "non-specific" thalamic nuclei, including the midline and intralaminar nuclei. Some studies have also suggested that the "specific" thalamic nuclei, including the ventral anterior and ventral lateral nuclei, have significant projections to the striatum in the monkey. The ventral anterior and ventral lateral nuclei receive the bulk of basal ganglia output from the basal ganglia and are primarily thought to relay this information to the cortex. The existence of thalamostriatal projections from the ventral anterior and ventral lateral nuclei suggests that the basal ganglia receives a direct feedback from the thalamus. As loss of function in basal ganglia circuits is associated with several neurologic disorders including Parkinson's disease and Huntington's disease and psychiatric disorders such as schizophrenia, how the thalamic input affects striatal output neurons and its relation to both the excitatory input from the cortex and the dopaminergic input from the midbrain may be crucial to understanding the pathophysiology of some of these disorders. The proposed experiments explore the organization of the thalamostriatal projections from the ventral nuclei and their relation to corticostriatal inputs from areas which also receive basal ganglia output.